Abstract:

Olive leaves are considered to have great potential as natural sources of antioxidants and phenolic compounds. In this study, dried olive leaves were extracted using four different solvents (water, methanol, ethanol, and 80:20(v/v) methanol-water) with ultrasonic-assisted extraction. The biochemical (total phenolics and flavonoids, total protein, free amino acids, total soluble, and reducing sugars) and antioxidant activities (CUPRAC, DPPH, FRAP, and FIC) of these extracts were evaluated. Total phenolics content was significantly affected by the different solvents and the highest total phenolics content was obtained in methanol-water (234 mg g-1) extraction. The highest total flavonoid (47 mg g-1) and total protein (5.1 mg g-1) content were obtained in methanol extraction. Yield of the free amino acids was lowest in ethanol (1.5 mg g-1), while it was highest in water (2.3 mg g-1) and methanol-water (2.2 mg g-1) extractions. The highest total soluble sugars were obtained from methanol-water (70.4 mg g-1) and ethanol (65.4 mg g-1) extractions, while the highest total reducing sugar contents were obtained from methanol (112.2 mg g-1) and methanol-water (111.6 mg g-1). While methanol-water extraction showed the highest antioxidant capacity with 0.63 mmol TR g-1 CUPRAC value, it also showed the strongest radical scavenging activity with 1.09 mmol TR g-1 DPPH radicals value and 0.065 mmol TR g-1 FRAP potential value. FIC capacity was higher in water than in other solvent extraction methods. Methanol and methanol-water solvents were the most effective solvents for measuring phenolic and antioxidant activities in olive leaves.

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